1. Field of the Invention
The invention relates to a method of detackifying secondary fiber paper pulps by treating the pulps with a water soluble terphthalate glycol terpolymer.
2. Description of the Prior Art
Various adhesive materials are present in paper fiber furnishes. These can include materials derived from the fibers themselves such as wood pitch, but more importantly and troublesome are adhesive contaminants present in secondary fiber furnishes. These adhesive contaminants, known in the trade as "stickies and tackies" cause numerous problems, both in terms of process and product performance. Specifically, the contaminants deposit on and adhere to machine surfaces throughout the papermachine disrupting operations. They can fill or plug forming fabrics and press felts. Large agglomerates can break loose from the equipment causing holes in the paper sheet or sheet breaks on the papermachine. If the contaminants are present in the paper, they will cause sheet defects or spots. This results in poor visual aesthetics of the paper, and because of poor surface properties can result in printing difficulties. The tackiness of these contaminants may cause adjacent sheets, when wound in roll form, to adhere to one another. This can cause tears, breaks and holes in converting processes.
Secondary fibers refers to recycled paper materials which are repulped to provide the papermaking furnish with raw material for the production of new papers. Sources of secondary fiber may include old newspaper (ONP), old corrugated containers (OCC), mixed office waste, computer printout (CPO), ledger, etc. These once-processed papers contain various types of adhesives (pressure sensitive, hot melts, etc.), inks, and coating binders. Coating binders can include the so called `white pitch` associated with the repulping of polyvinyl acetate and styrene butadiene coated broke. An extensive list of natural and synthetic adhesives found in different grades of paper is described in the article, "Stickies Control by Detackification", Robert D. Moreland, 1986 Pulping Conference, pp. 193-196. This article also describes in some detail the problem solved by the present invention. A further description of stickies and related problems are found in the disclosures of U.S. Pat. Nos. 4,956,051 and 4,923,566. The disclosures of these references are incorporated herein by reference.
To deal with the problem of stickies and tackies, a number of strategies have been employed by papermakers. These strategies include mechanical and chemical means to either remove or passivate the contaminants. Mechanical means of removing the contaminants include slotted pressure screens, hydrocyclones, and cleaners of various types. Also thermal/mechanical dispersion units are employed to break the contaminants into micron sized particles, which are then difficult to detect in the final sheet. Despite these techniques 100% removal of contaminants by mechanical means cannot be accomplished.
Chemically, several approaches are taken, including passivation or detackification of the sticky contaminant surfaces. Such detackification agents include inorganic materials such as talc and zirconium compounds, organic materials such as polyvinyl alcohol, and hydrophobic synthetic fibers such as polypropylene. In addition, various dispersants may be used to prevent the contaminants from agglomerating. The small dispersed contaminants may be fixed to the paper sheet by the use of cationic polymers. Finally if the contaminant problem becomes severe, solvents will be used to wash and remove the materials from machine surfaces and clothing.